Re: Concurrent request handling
Re: Concurrent request handling
- Subject: Re: Concurrent request handling
- From: Chuck Hill <email@hidden>
- Date: Tue, 05 Apr 2011 10:48:10 -0700
Hi Mark,
On Apr 4, 2011, at 11:20 PM, Mark Wardle wrote:
> Hi all,
>
> There have been a number of threads discussing this runtime option. I
> think the consensus opinion was that although it is off by default, it
> is better switched on.
I think it is off by default to match the previous (now ancient) functionality.
> Presumably there are some basic additional rules to follow.
The EOF Commandments (as usual) plus:
Don't Do Stupid Things
> For instance, AFAIK components will not be shared by multiple threads
> as they will be instantiated as one goes along or will be returned
> from the page cache as part of a single session - and as one session
> will be handled by only one thread, this is fine. How does concurrent
> handling interact with stateful and stateless components?
Stateful are always session specific so safe by design. Stateless are also safe, transparently, see Practical WebObjects for the details if you want.
> Perhaps more of an issue is that code within my EOF classes may be
> executed by more than one thread at a time. I use lazy initialisation
> but there is a race condition there. Fortunately, most of the time
> there are no side-effects and running that code twice would have no
> significant deleterious effect. For situations where it would matter I
> would assume protecting lazy initialisation with a double check and a
> synchronised block for the inner check would be fine? Is that
> interpretation correct?
I think that synchronised is what you want.
> Are there other commandments?
Don't Do Stupid Things :-) Which boils down to don't share objects that are not thread-safe, or writable data, at the global level unless you have appropriate protection. Global being either static members or instance variables on your application. Shared, non-thread safe formatters are a common mistake.
Chuck
--
Chuck Hill Senior Consultant / VP Development
Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems.
http://www.global-village.net/products/practical_webobjects
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